A high efficiency gas turbine engine requires high inlet gas temperatures to the turbine. Accordingly first stage vanes and blades are operating near the maximum temperature for which they may be designed.
These vanes and blades require cooling for long term survival. A common method is to use high pressure air from the compressor which is supplied internally to the vane or blade airfoils for cooling the structure.
Several methods for using this cooling air to cool the surface are known. Film cooling of the external surface is the achieved by permitting the air to exit through the surface in a controlled manner to flow along the outside film of the blade. Convection cooling of the internal surface is also used, with trip strips sometimes located to improve the heat transfer. Impingement cooling is also used by directing high velocity flow substantially perpendicular to the internal surface of the airfoil being cooled.
In Japanese Patent Application 58-197402(A) air is impinged on the internal wall of a blade at a location between projections. These projections extend from the internal surface of the blade wall the full height of the air passage.